The invention relates to the field of communications systems and, more specifically, to a method and apparatus of forming and demultiplexing a very high density WDM signal.
Within the context of a high density wave division multiplex (WDM) access system, the cost and efficacy of passive WDM demultiplexers capable of retrieving desired multiplexed WDM streams as substreams becomes prohibitive. For example, consider a thousand channels where each channel operates at 50 Mbits/sec to produce an aggregate bit rate of 50 Gbits/sec. This may not be practical. In the case of a pure time division multiplex (TDM) system, each of a respective one thousand receivers would require a 50 gigabit per second TDM demultiplexer. In the case of a pure WDM version of the system, very close channel spacing is required and large numbers of wavelength demultiplexers capable of separating such very closely spaced channels (approximately 10 GHz) are required. Such a WDM system also may not be very practical.
It is therefore seen to be desirable to provide a hybrid WDM/TDM demultiplexing system suitable for use in a high density WDM system. More particularly, it is seen to be desirable to provide such a hybrid TDM/WDM demultiplexing system within a chirped pulse WDM system (CPWDM).
The invention comprises a method and apparatus for preparing groups of low duty cycle WDM transmission channels such that each group can be demultiplexed either via conventional WDM (e.g., by optically filtering each channel and receiving that channel at its line rate) or via TDM (e.g., directing an entire group of WDM channels onto a signal higher speed detector, receiving them all and demultiplexing the channels in a temporal (electronic) domain). The invention provides several advantages; namely, the replacement of high cost, very fine optical demultiplexers with cheaper electronic demultiplexers, straight forward implementation of various bit rate or scalable delivery per user (e.g., delivery of a single optical channel at channel rate and/or TDM delivery of N channels at a rate of N times the channel rate), and a direct path to higher channel count upgradability. These advantages may be simultaneously obtained using a transmitter formed according to the teachings of the present invention. Advantageously, the invention also enables a flexible bandwidth allocation scheme in which customer bandwidth requirements may be easily scaled up (or down) by the proper selection of optical filters at respective customer receivers.
The invention comprises a method and apparatus for demultiplexing a high density wave division multiplex (WDM) signal using coarse WDM passive demultiplexing elements and electronic time division multiplexing (TDM) demultiplexing elements. In this manner, the WDM nature of the transmission network is fully maintained and easily upgraded with finer WDM demultiplexers as desired. Additionally, the invention scales to accommodate various bandwidth users or multiple bandwidth users. A dual WDM/TDM demultiplexer may be simultaneously employed within the context of the present invention.